Calculation: multiplying and dividing by 10 or 100

Introduction

Use place-value knowledge to develop strategies for multiplying/dividing by 10 and 100. Generalise about the product or quotient when a factor or the dividend is made 10 or 100 times bigger/smaller.

Teaching points

• Teaching point 1: Finding 10 times as many is the same as multiplying by 10 (for positive numbers); to multiply a whole number by 10, place a zero after the final digit of that number.
   
• Teaching point 2: To divide a multiple of 10 by 10, remove the final zero digit (in the ones place) from that number.
   
• Teaching point 3: Finding 100 times as many is the same as multiplying by 100 (for positive numbers); to multiply a whole number by 100, place two zeros after the final digit of that number.
   
• Teaching point 4: To divide a multiple of 100 by 100, remove the final two zero digits (in the tens and ones places) from that number.
   
• Teaching point 5: Multiplying a number by 100 is equivalent to multiplying by 10, and then multiplying the product by 10. Dividing a multiple of 100 by 100 is equivalent to dividing by 10, and then dividing the quotient by 10.
   
• Teaching point 6: If one factor is made 10 times the size, the product will be 10 times the size. If the dividend is made 10 times the size, the quotient will be 10 times the size.
   
• Teaching point 7: If one factor is made 100 times the size, the product will be 100 times the size. If the dividend is made 100 times the size, the quotient will be 100 times the size.